1. Field of the Invention
The present invention is in general related to an integrated circuit. More specifically, the present invention is related to a four-quadrant three-input multiplier that can receive three distinct signals and multiply them together. Such a scheme can be utilized under low-voltage conditions. Four-quadrant three-input multipliers can be used as modulators, demodulators, triplers, and to synthesize nonlinear functions.
2. Description of the Invention
Multipliers are essential components that serve as building blocks for calculating the product of two or more different signals. In bipolar transistor technology, Gilbert cells are usually used to build a four-quadrant multiplier. But in MOS transistor technology, four approaches have emerged. The first approach, similar to the case of bipolar technology, is to use Gilbert cells to build a four-quadrant multiplier. The second approach is to use the properties of MOS transistors operated in the saturation region to design multipliers. The saturation region is also called an active region where the drain current value is proportional to the square of the gate-drain voltage value. The third approach is to use the properties of MOS transistors operated in the linear region to design multipliers. The linear region is also called the triode region where the drain current value is linearly proportional to the gate-source voltage while the drain-source voltage is a constant. The fourth or last approach is to use the properties of MOS transistors operated in the subthreshold region to design multipliers.
Conventionally, two Gilbert cells or other type of multipliers that are serially or cascadedly connected are usually utilized to constitute a three-input multiplier. However, such a configuration can not concurrently receive all three input signals. The output signal from the previous Gilbert cell, which receives the first two input signals, is temporally incompatible with the last input signal in the subsequent Gilbert cell, due to time delay in the previous Gilbert cell. In addition, a cascaded-type configuration has a complex structure.
Increasingly smaller size and low power operation are the trends of integrated circuits in the future. Thus, it is essential to make integrated circuits operate with low voltage supplies and low power consumption.